SHAPE MEMORY STAINLESS STEELS WITH RARE EARTH ELEMENTS Ce AND La

ABSTRACT

Shape memory stainless steels with rare earth elements Cerium (Ce) and Lanthanum (La) are disclosed. In one embodiment, raw materials including Manganese (Mn), Silicon (Si), Chromium (Cr), Nickel (Ni), Carbon (C), Ce, La and Iron (Fe) are melted to form a molten alloy of the shape memory stainless steels with rare earth elements Ce and La. Further, the molten alloy is solidified to form an ingot. Furthermore, the ingot is subjected to nondestructive evaluation to assess internal soundness of the ingot. In addition, the evaluated ingot is homogenized to form homogenized shape memory stainless steels with rare earth elements Ce and La.

RELATED APPLICATIONS

Benefit is claimed under 35 U.S.C 119(a)-(d) to Foreign ApplicationSerial No. 4525/CHE/2011, filed in INDIA entitled “SHAPE MEMORYSTAINLESS STEELS WITH RARE EARTH ELEMENTS Ce AND La” by AirbusEngineering Centre India, filed on Dec. 22, 2011, which is hereinincorporated in its entirety by reference for all purposes.

FIELD OF TECHNOLOGY

The present subject matter relates to shape memory stainless steels.More particularly, the present subject matter relates to shape memorystainless steels with rare earth elements Cerium (Ce) and Lanthanum(La).

BACKGROUND

Shape memory alloys are a promising class of advanced materials used inmany high technology applications, such as aerospace, electronics, andbiotechnology. The shape memory alloys at a high temperature can be usedas functional materials, such as actuators for aircraft engines,automobiles and pipe couplings. Further, the shape memory alloys areused to absorb wind energy. Typically, Nickel-Titanium (Ni—Ti) andCopper (Cu) based shape memory alloys have been used in such hightechnology applications. Even though the Nickel-Titanium (Ni—Ti) andCopper (Cu) based shape memory alloys have good shape memory effect,however their mechanical properties are lower and are significantly moreexpensive to produce when compared with shape memory stainless steels.Further, machinability of the Ni—Ti based shape memory alloys isrelatively poor when compared with the shape memory stainless steels.

Generally, the shape memory stainless steels are cheaper alternatives tothe expensive Ni—Ti and Cu based shape memory alloys. The existing shapememory stainless steels exhibit good shape memory effect, mechanicalproperties, machinability, weldability and corrosion resistance.However, the shape memory effect of the shape memory stainless steels isnot as good as the Ni—Ti and Cu based shape memory alloys.

It is well known that the shape memory effect in Iron (Fe) based shapememory alloys is associated with the transformation of face centredcubic austenite (γ) to hexagonal closed packed (hcp) ε—martensite. Thetransformation can be divided into two components, such as one involvingformation of ε—martensite when cooled below a martensite starttemperature (Ms) and the other involving stress induced transformationof austenite. There are different opinions on the effect of thermalmartensite on recovery strain of the Fe based shape memory alloys. Onetechnique that is used to reduce an incidence of thermal martensite isto reduce Ms by decreasing the austenite grain size, such as addition ofgrain refining elements, thermo-mechanical treatments and so on.

SUMMARY

Shape memory stainless steels with rare earth elements Cerium (Ce) andLanthanum (La) are disclosed. According to one aspect of the presentsubject matter, the shape memory stainless steels with rare earthelements include Manganese (Mn), Silicon (Si), Chromium (Cr), Nickel(Ni), Carbon (C), Ce, La and Iron (Fe). The shape memory stainlesssteels with rare earth elements Ce and La include, by weight, about 15to 17% of Mn, about 5 to 6% of Si, about 9 to 12% of Cr, about 8 to 10%of Ni, about 0.03 to 0.06% of C, about 0.10 to 0.50% of Ce, about 0.5 to1.0% of La and the balance being Fe.

According to another aspect of the present subject matter, raw materialsincluding Mn, Si, Cr, Ni, C, Ce, La and Fe are melted to form a moltenalloy of the shape memory stainless steels with rare earth elements Ceand La. Further, the molten alloy is solidified to form an ingot.Furthermore, the ingot is subjected to nondestructive evaluation toassess internal soundness of the ingot. In addition, the evaluated ingotis homogenized to form homogenized shape memory stainless steels withrare earth elements Ce and La. Moreover, a semi-finished product isformed from the homogenized shape memory stainless steels with rareearth elements Ce and La. Also, a desired component is formed from thesemi-finished product.

The method disclosed herein may be implemented in any means forachieving various aspects. Other features will be apparent from theaccompanying drawings and from the detailed description that follow.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments are described herein with reference to the drawings,wherein:

FIG. 1 illustrates a flow diagram of an exemplary method of formingshape memory stainless steels with rare earth elements Cerium (Ce) andLanthanum (La); and

FIG. 2 is a table including a range, by weight, of each element in theshape memory stainless steels with rare earth elements Ce and La,according to one embodiment.

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

DETAILED DESCRIPTION

Shape memory stainless steels with rare earth elements Cerium (Ce) andLanthanum (La) are disclosed. In the following detailed description ofthe embodiments of the present subject matter, references are made tothe accompanying drawings that form a part hereof, and in which areshown by way of illustration specific embodiments in which the presentsubject matter may be practiced. These embodiments are described insufficient detail to enable those skilled in the art to practice thepresent subject matter, and it is to be understood that otherembodiments may be utilized and that changes may be made withoutdeparting from the scope of the present subject matter. The followingdetailed description is, therefore, not to be taken in a limiting sense,and the scope of the present subject matter is defined by the appendedclaims.

FIG. 1 illustrates a flow diagram 100 of an exemplary method of formingshape memory stainless steels with rare earth elements Ce and La. Atblock 102, raw materials including Manganese (Mn), Silicon (Si),Chromium (Cr), Nickel (Ni), Carbon (C), Ce, La and Iron (Fe) are added.In one embodiment, as shown in FIG. 2, the shape memory stainless steelswith rare earth elements Ce and La include, by weight, about 15 to 17%of Mn, about 5 to 6% of Si, about 9 to 12% of Cr, about 8 to 10% of Ni,about 0.03 to 0.06% of C, about 0.10 to 0.50% of Ce, about 0.5 to 1.0%of La and the balance being Fe. At block 104, the added raw materialsare melted to form a molten alloy of the shape memory stainless steelswith rare earth elements Ce and La. In one embodiment, the added rawmaterials are melted at a temperature of about 1600° C. to form themolten alloy. In this embodiment, the added raw materials are meltedconventionally or using vacuum induction at the temperature of about1600° C. to form the molten alloy.

At block 106, the molten alloy is solidified to form an ingot. In oneembodiment, the molten alloy is solidified by cooling to form the ingotof a desired shape. At block 108, the ingot is subjected tonondestructive evaluation to assess internal soundness of the ingotbased on quality parameters, such as internal defects, voids, cracks,cavities and the like. In one embodiment, the nondestructive evaluationuses gamma radiography. At block 110, the evaluated ingot is homogenizedto form homogenized shape memory stainless steels with rare earthelements Ce and La. In one embodiment, the evaluated ingot ishomogenized by heating the evaluated ingot at a temperature in a rangeof about 1050° C. to 1150° C. for about 6 hours to form the homogenizedshape memory stainless steels with rare earth elements Ce and La. Atblock 112, a semi-finished product is formed from the homogenized shapememory stainless steels with rare earth elements Ce and La. Exemplarysemi-finished product includes a rolled product, a forged product andthe like. At block 114, a desired component is formed from thesemi-finished product. In one embodiment, the semi-finished product iscold worked or machined to form the desired component. Exemplary desiredcomponent includes an actuator for an aircraft engine, an automobilecomponent, a pipe coupling and the like.

In one embodiment, to measure shape memory effect of the shape memorystainless steels with rare earth elements Ce and La, thin sheets of thehomogenized shape memory stainless steels with rare earth elements Ceand La are made and then small strips are extracted from the thinsheets. In one embodiment, strips with different lengths are extractedfrom the thin sheets to measure the shape memory effect. Further, thestrips are bent into a semicircular shape on mandrels with differentdiameters at a room temperature with the ends of strips perpendicular tohorizontal straight line. Furthermore, pre-strain (ε_(p)) is computedfor each strip using an equation:

ε_(p) =t/d

where t is thickness of the strips and d is diameter of the semicircularshapes of a respective strip.

The strips are then allowed to recover at a temperature in a range about400° C.-450° C. In addition, a degree of shape recovery (η_(SME)) foreach strip is computed using an equation:

η_(SME)=((90−θ)/90)×100

where θ is a residual angle.

Also, the shape memory effect (also referred as a net reversible strain(ε_(R))), in percentage, for each strip is computed using an equation:

ε_(R)=ε_(P)×η_(SME).

Referring now to FIG. 2, a table 200 including a range, by weight, ofeach element in the shape memory stainless steels with rare earthelements Ce and La, according to one embodiment. In the table 200, thefirst row includes various elements in the shape memory stainless steelswith rare earth elements Ce and La, such as Mn, Si, Cr, Ni, C, Ce, Laand Fe. Further in the table 200, the second row includes the range, byweight, of each element in the shape memory stainless steels with rareearth elements Ce and La. Using the range of the elements, in the table200, one can form multiple shape memory stainless steels with rare earthelements Ce and La.

In various embodiments, the method described in FIGS. 1 and 2 enables toform the shape memory stainless steels with rare earth elements Ce andLa. The shape memory stainless steels with rare earth elements Ce and Laare cheaper compared to existing shape memory alloys. Further, the shapememory stainless steels with rare earth elements Ce and La have goodmechanical properties, machinability, weldability and corrosionresistance.

Although the present embodiments have been described with reference tospecific example embodiments, it will be evident that variousmodifications and changes may be made to these embodiments withoutdeparting from the broader spirit and scope of the various embodiments.

What is claimed is:
 1. Shape memory stainless steels with rare earthelements Cerium (Ce) and Lanthanum (La), which comprise, Manganese (Mn),Silicon (Si), Chromium (Cr), Nickel (Ni), Carbon (C), Ce, La and Iron(Fe).
 2. The shape memory stainless steels of claim 1, wherein the shapememory stainless steels with rare earth elements Ce and La comprise, byweight, about 15 to 17% of Mn, about 5 to 6% of Si, about 9 to 12% ofCr, about 8 to 10% of Ni, about 0.03 to 0.06% of C, about 0.10 to 0.50%of Ce, about 0.5 to 1.0% of La and the balance being Fe.
 3. The shapememory stainless steels of claim 2, wherein the shape memory stainlesssteels with rare earth elements Ce and La further comprise: unavoidableimpurities.
 4. A method of forming shape memory stainless steels withrare earth elements Cerium (Ce) and Lanthanum (La), comprising: meltingraw materials including Manganese (Mn), Silicon (Si), Chromium (Cr),Nickel (Ni), Carbon (C), Ce, La and Iron (Fe) to form a molten alloy ofthe shape memory stainless steels with rare earth elements Ce and La;solidifying the molten alloy to form an ingot; subjecting the ingot tonondestructive evaluation to assess internal soundness of the ingot; andhomogenizing the evaluated ingot to form homogenized shape memorystainless steels with rare earth elements Ce and La.
 5. The method ofclaim 4, wherein the shape memory stainless steels with rare earthelements Ce and La comprise, by weight, about 15 to 17% of Mn, about 5to 6% of Si, about 9 to 12% of Cr, about 8 to 10% of Ni, about 0.03 to0.06% of C, about 0.10 to 0.50% of Ce, about 0.5 to 1.0% of La and thebalance being Fe.
 6. The method of claim 4, wherein homogenizing theevaluated ingot to form the homogenized shape memory stainless steelswith rare earth elements Ce and La comprises: homogenizing the evaluatedingot by heating the evaluated ingot at a temperature in a range ofabout 1050° C. to 1150° C. for about 6 hours to form the homogenizedshape memory stainless steels with rare earth elements Ce and La.
 7. Themethod of claim 4, wherein the nondestructive evaluation comprisesnondestructive evaluation using gamma radiography.
 8. The method ofclaim 4, wherein melting the raw materials to form the molten alloycomprises: adding the raw materials; and melting the added raw materialsat a temperature of about 1600° C. to form the molten alloy.
 9. Themethod of claim 8, wherein melting the added raw materials at thetemperature of about 1600° C. comprises: conventional melting of theadded raw materials at the temperature of about 1600° C.
 10. The methodof claim 8, wherein melting the added raw materials at the temperatureof about 1600° C. comprises: vacuum induction melting of the added rawmaterials at the temperature of about 1600° C.
 11. The method of claim4, wherein solidifying the molten alloy to form the ingot comprises:solidifying the molten alloy by cooling to form the ingot of a desiredshape.
 12. The method of claim 4, further comprising: forming asemi-finished product from the homogenized shape memory stainless steelswith rare earth elements Ce and La.
 13. The method of claim 12, whereinthe semi-finished product comprises a rolled product or a forgedproduct.
 14. The method of claim 12, further comprising: forming adesired component from the semi-finished product.
 15. The method ofclaim 14, wherein the desired component is an actuator for an aircraftengine, an automobile component and a pipe coupling.